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R Kandiyoti – 1st expert on this subject based on the ideXlab platform
an investigation of the reactivity of chars formed in fluidized Bed Gasifiers the effect of reaction conditions and particle size on coal char reactivityEnergy & Fuels, 2006Co-Authors: A Cousins, N Paterson, D. R. Dugwell, R KandiyotiAbstract:
Coal-derived chars formed during air-blown gasification processes may rapidly lose reactivity, and this can limit the extent of their conversion. To study this effect, a laboratory-scale fluidized Bed reactor has been modified to enable char samples to be prepared under strictly controlled conditions of temperature, pressure, particle size, gaseous environment, and residence time. This has been used to gain an insight into the deactivation of the chars as they form and during their subsequent residence time in the Bed of the gasifier. The work shows that the char reactivity declines rapidly during its formation as part of the pyrolysis of the coal. This is thought to result from the rapid deposition of secondary, unreactive char within the pores of the material. In this work, it has been shown to occur within the initial 10 s in the reactor, but in reality, this effect probably occurred within 1 s. Temperature, pressure, and particle size have an impact on this process. Subsequently, and over a longer tim…
an investigation of the reactivity of chars formed in fluidized Bed Gasifiers equipment development and initial testsEnergy & Fuels, 2006Co-Authors: A Cousins, N Paterson, D. R. Dugwell, R KandiyotiAbstract:
Chars formed during air and oxygen blown gasification processes have a low reactivity. This is due to changes that occur in the structure and morphology of the original coal during heating. In part, the changes depend on conditions prevailing during the pyrolysis stage and partly on the length of time spent at peak temperature. Previous work in this laboratory has highlighted that the gasification reactivity of a char depends on the conditions of its formation. This means that chars must be prepared under realistic conditions when conducting laboratory scale reactivity studies that are intended to support a larger scale development. This is not easy to do and requires the development of dedicated methods for preparing the char. In this paper, the development of a laboratory-scale test, based on a laboratory-scale spouted Bed gasifier, is descriBed that is able to prepare chars under conditions that represent those in an air-blown gasifier. The reactivity of the prepared chars is then examined to identify …
Henrik Thunman – 2nd expert on this subject based on the ideXlab platform
bark as feedstock for dual fluidized Bed Gasifiers operability efficiency and economicsInternational Journal of Energy Research, 2019Co-Authors: Johan Ahlstrom, Alberto Alamia, Anton Larsson, Claes Breitholtz, Simon Harvey, Henrik ThunmanAbstract:
The demand for biofuels and biochemicals is expected to increase in the future, which will in turn increase the demand for biomass feedstock. Large gasification plants fueled with biomass feedstock are likely to be a key enabling technology in a resource-efficient, bio-based economy. Furthermore, the costs for producing biofuels and biochemicals in such plants could potentially be decreased by utilizing inexpensive low-grade residual biomass as feedstock. This study investigates the usage of shredded tree bark as a feedstock for the production of biomethane in the GoBiGas demonstration plant in Gothenburg, Sweden, based on a 32 MWth industrial dual fluidized Bed gasification unit. The plant was operated with bark feedstock for 12 000 hours during the period 2014 to 2018. Data from the measurement campaign were processed using a stochastic approach to establish the plant’s mass and energy balances, which were then compared with operation of the plant with wood pellets. For this comparison, an extrapolation algorithm was developed to predict plant performance using bark dried to the same moisture content as wood pellets, ie, 8%w.b. Plant operation with bark feedstock was evaluated for operability, efficiency, and feedstock-related cost. The gas quality achieved during the test period was similar to that obtained for operation with wood pellets. Furthermore, no significant ash sintering or agglomeration problems were observed more than 750 hours of operation. The calculated biomass-to-biomethane efficiency is 43% to 47% (lower heating value basis) for operation with wet bark. However, the predicted biomass-to-biomethane efficiency can be increased to 55%–65% for operation with bark feedstock dried to 8% moisture content, with corresponding feedstock costs in the range of 24.2 to 32.7 EUR/MWh; ie, a cost reduction of about 40% compared with wood pellets.
volatile gases from biomass pyrolysis under conditions relevant for fluidized Bed GasifiersJournal of Analytical and Applied Pyrolysis, 2017Co-Authors: Daniel Santos Felix Neves, Henrik Thunman, Arlindo Matos, L A C Tarelho, Anton Larsson, Martin SeemannAbstract:
The pyrolytic volatiles released from a converting biomass particle are investigated in this work through laboratorial fluidized Bed experiments simulating conditions typical of large-scale Gasifiers. Two types of wood (eucalyptus and pine) and two types of pellets (forest residues and wood) with particles of 6-8 mm in diameter are fed over the hot bubbling Bed at temperatures within 600-975 degrees C. The resultant major pyrolytic products (char, soot, liquids and permanent gas) are collected to verify the overall mass balance, and the composition of the permanent gas is resolved in C3H8, C2H6, C2H4, CH4, CO2, CO, and H-2. Primary pyrolysis of the parent fuel particles is essentially complete at 600 degrees C and further increase of the temperature mainly leads to a progressive change in the composition of the volatile gas mixture. Although the gas release does not attain thermodynamic equilibrium under the conditions tested, our results show that the yields of CO2 and light hydrocarbons go through maxima as temperature increases to give rise to CO and H-2 as the preferable species at high temperatures. As a whole, the gas composition evolves in such a way that the corresponding lower heating value steadily increases with temperature increase, from about 11 MJ/kg at 600 degrees C to above 17 MJ/kg at 950 degrees C. Furthermore, the yields of key gas species were found well correlated to each other (C2H4 vs. CH4, CH4 vs. CO and H-2 vs. CO), with the relation between the yields of H-2 and CO being slightly dependent on the composition of fuel.
process simulation of dual fluidized Bed Gasifiers using experimental dataEnergy & Fuels, 2016Co-Authors: Alberto Alamia, Henrik Thunman, Martin SeemannAbstract:
Process simulation of a dual fluidized Bed (DFB) gasifier is challenging, owing to the high degree of freedom inherent to the operation of the double-reactor system and the complexity of the reactions therein. We propose a method for simulation of the gasifier based on the analysis of experimental data and of the total uncertainty associated with them. The overall aim is to use data from the large amount of pilot and demonstration Gasifiers in the analysis and optimization of gasification-based processes. In the method proposed a set of fuel conversion variables and their associated uncertainties are calculated using a stochastic approach that takes into account the effect of unclosed mass balance, incomplete characterization of the raw gas compounds and measurement errors. Subsequently, these fuel conversion variables are used to simulate the gasifier in a flowsheet model developed in Aspen Plus. The results include the evaluation of critical parameters, such as, gasifier efficiency, char gasification, a…
Animesh Dutta – 3rd expert on this subject based on the ideXlab platform
equilibrium modeling of gasification gibbs free energy minimization approach and its application to spouted Bed and spout fluid Bed GasifiersEnergy Conversion and Management, 2008Co-Authors: S Jarungthammachote, Animesh DuttaAbstract:
Spouted Beds have been found in many applications, one of which is gasification. In this paper, the gasification processes of conventional and modified spouted Bed Gasifiers were considered. The conventional spouted Bed is a central jet spouted Bed, while the modified spouted Beds are circular split spouted Bed and spout-fluid Bed. The Gibbs free energy minimization method was used to predict the composition of the producer gas. The major six components, CO, CO2, CH4, H2O, H2 and N2, were determined in the mixture of the producer gas. The results showed that the carbon conversion in the gasification process plays an important role in the model. A modified model was developed by considering the carbon conversion in the constraint equations and in the energy balance calculation. The results from the modified model showed improvements. The higher heating values (HHV) were also calculated and compared with the ones from experiments. The agreements of the calculated and experimental values of HHV, especially in the case of the circular split spouted Bed and the spout-fluid Bed were observed.